The response of the vegetation and soils of the higher latitude forests and tundra ecosystems to an anticipated climate change is investigated using two alternative approaches to calculate the resulting change in the total carbon content (TCC) of the vegetation and the soils: On the one hand a BGC (bio-geochemical-cycle) model, in this case the FBM (Frankfurt Biosphere Model), where the ecosystem response is entirely due to the ecophysiological response of the vegetation and the ecological response of the soils. On the other hand a biome or ” rule-based” model, in this case the BIOME model, which allows for the determination of the occurrence of a specific biome type from a given climatic situation assuming equilibrium conditions. Within the FBM prognosis net primary production and TCC are reduced both for needle leaved and broad leaved forests if the CO2-fertilisation effect is not taken into account. When the CO2-fertilisation effect is taken into consideration NPP, standing biomass and soil carbon are increased in a future greenhouse climate. Although there is a considerable shift of the biomes in response to the greenhouse climate within the BIOME approach, the TCC in the investigated northern biomes stayed more or less constant. This is due to a decrease in biomass in the southern regions of today's temperate forests compensating the biomass increase by the northward shift of the taiga border.